1. Field of the Invention
The present invention relates to electronic flash control units used with cameras and imaging devices and, more particularly, to flash control devices which utilize TTL type light adjustment components and methods.
2. Description of the Related Art
Automatic light adjustment devices found in flash illumination units (also referred to as "SB" type flash adjustment and control devices) have been designed, for the most part, to be used with single lens reflex (SLR) cameras. Such adjustment devices utilize control methods in which an emitted light beam reflected by a subject passes through a photographic or taking lens (i.e., an objective lens) so that photometry is performed in real time based on the light reflected for photographic operations. As such, when an optimum amount of light has been emitted, reflected, and detected, flash light emission is stopped. And, because photometry is performed based on a light beam which passes through a photographic lens, there is no displacement or parallax between a subject region which is to be photographed and a subject region for which photometry is performed. As a result, a photographer can take advantage of automatically set aperture values, etc., without slowing or impeding photographic operations.
Despite the effectiveness of light emission control systems commonly used with single lens reflex cameras, in cameras and imaging devices that utilize TTL light adjustment components and methods, the diffusion characteristics of a photographic surface (e.g., a silver salt based film or a solid state imaging element, etc.) are based on an assumption that such a photographic surface is capable of complete light diffusion. And, in the case that the diffusion characteristics markedly differ from a completely diffusing surface light emission control properties, among others, are poor to the point that poor photographic results may be obtained.
For example, with solid state imaging elements used as photographic imaging surfaces of electronic cameras, the diffusing characteristics of the imaging elements themselves are poor and, due to the effects of cover glass and the like disposed in its foreground, the diffusion characteristics depart markedly from those of a completely diffusing surface. As such, in electronic and digital type cameras that utilize TTL light adjustment structures and methods, suitable exposures were not obtained.
In order to solve such problems and to further realize the benefits of TTL type light adjustment systems and methods, especially in non-SLR type cameras, various solutions have been proposed. One such exemplary system is shown and described in Japanese Laid-Open Patent Publication JP-A-9-90461. Such a system seeks to control camera exposures at the time of SB use.
A system like that shown in the aforementioned Japanese patent publication is shown in a drawing figure identified as FIG. 20 which is attached to this patent document. In particular, a first operation 51 (for example, a camera operation commencing upon half-depression of a shutter button, etc.) includes photometry determination via photometric means 52 and range finding and aperture control via means 53.
During a second operation 54 (for example, a camera operation commencing upon full-depression of a shutter button, etc.), preliminary light emission by an SB light emission unit 57 occurs. Simultaneously, a preliminary exposure 55, based on the result of the preliminary exposure 55, sets the SB light emission amount of the light emission unit 57 for the time of a main exposure 56.
Unfortunately, in devices like those mentioned above, significant time was spent gathering preliminary illumination data and generating corresponding outputs. Such time was necessary as reliable calculation of a main illumination period for flash based imaging operations required successive preliminary flashes to reach a qualified result. Due to the number of signals involved and the computations necessary to reliably compute a main illumination period, imaging device (camera, etc.) operations were slowed. Such problems were compounded by the fact that imaging devices commonly utilized a single flash source for both preliminary and main illumination.
Thus, there exists a need to provide new and improved flash device control devices and methods that reliably reduce the amount of time taken to compute a main illumination period without unduly reducing image quality and the like. To be viable, such flash control devices and methods must be suited to be implemented in self-contained camera assemblies and in separately attachable flash units.